Evaluation of rat hepatic 2E1 activity in function of age, sex and inducers: choice of an experimental model capable of testing the hepatotoxicity oflow molecular weight compounds

The aim of this work on rat hepatic P450 2E1 activity was to seek the most suitable experimental model to study the role of cytochrome P450 2E1 in the metabolism of industrial chemicals. Two sets of experiments were devoted t o selecting the age and sex of animals and to estimating the response of ma le and female rats to different inducers. In the first set, the effect of t hree inducers (fasting; ethanol; acetone) was studied in male rats aged 5, 7 and 9 weeks. In the second set, the effect of different inducers, namely beta-naphthoflavone (BNF), phenobarbital (PB), ethanol, acetone and pyridin e, on PNP and chlorzoxazone (CLZO) hydroxylase activities was studied in 7 week old male and female rats. The results demonstrate firstly that microso mal p-nitrophenol (PNP) hydroxylase activity significantly decreases in con trol male rats in inverse function of age, and secondly that induction by e thanol decreases with age. The PNP hydroxylase activity level of controls a nd the significant increases in PNP hydroxylase activity observed in 7 week old male rats show that this is the most suitable age for the second set o f experiments. In this second set, it was shown that P450 1A (induced by BN F) is involved in CLZO hydroxylase activity only. PB increased the hydroxyl ase activities in male and female rats by about 1.5 and 1.7 times those of the controls, respectively. The effects of P450 2E1 inducers in function of sex show that male rats exhibited more significant increases in PNP and CL ZO hydroxylase activities than female. The specificity of these two substra tes is discussed. Neither of these two reactions was specifically catalysed by P450 2E1, but PNP may be considered as the most specific and the least sensitive substrate. In addition, the linear relationship observed between the two substrates (PNP and CLZO) showed a good correlation between their a ctivities (r = 0.90, P < 0.001). In conclusion, these results suggest the u se of the 7 week old male rat as the experimental model to study the role o f cytochrome P450 2E1 in the hepatotoxicity of low molecular weight industr ial chemicals. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.